This invention relates to resolvers, and more particularly, to an improved resolver with redundant excitation windings.
Certain specific applications require a shaft position, feedback device which is redundant for safety purposes, but must be inexpensive in order to be feasible for the application. Typically, two independent feedback devices are needed to achieve the redundancy required for the application. In order to minimize cost, it is desirable to wind a single resolver stator lamination stack with two excitation windings and two sets of output windings which are coupled through a single rotor rather than providing separate stator lamination stacks and separate rotor pieces. Using conventional winding techniques with two resolver windings on a single core, excited independently, results in cross coupling between the redundant windings preventing them from being totally independent from one another. This results in a distorted wave form from the output windings which causes the decoded feedback information to be inaccurate.
An object of this invention is the provision of a resolver with redundant windings that minimizes the cross coupling between the windings while, at the same time, maintaining symmetrical output signals.
Briefly, this invention contemplates the provision of a resolver with redundant excitation windings in which only a single excitation winding is energized externally at a given time. Cross coupling from the externally energized winding induces a voltage in the other excitation winding. A control circuit monitors the voltage on the redundant winding and switches the excitation to the redundant winding in the event of a failure of the externally excited winding or its excitation source.